Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010

17.

1.

Steinbach HL. The roentgen appearance of osteoporosis. Radiol Clin

North Am 1964;2:191–207

18.

2.

Kamholtz R, Sze G. Current imaging in spinal metastatic disease.

Semin Oncol 1991;18:158–169

3.

Fayad LM, Johnson P, Fishman EK. Multidetector CT of musculo-

skeletal disease in the pediatric patient: principles, techniques, and

19.

clinical applications. Radiographics 2005;25:603–618

4.

Fayad LM, Bluemke DA, Fishman EK. Musculoskeletal imaging with

20.

computed tomography and magnetic resonance imaging: when is

computed tomography the study of choice? Curr Probl Diagn Radiol

2005;34:220–237

5.

Genant HK, Wilson JS, Bovill EG, Brunelle FO, Murray WR, Rodrigo JJ.

21.

Computed tomography of the musculoskeletal system. J Bone Joint

Surg Am 1980;62:1088–1101

6.

Wilson JS, Korobkin M, Genant HK, Bovill EG Jr. Computed tomo-

graphy of musculoskeletal disorders. AJR Am J Roentgenol

22.

1978;131:55–61

7.

Geijer M, El-Khoury GY. MDCT in the evaluation of skeletal trauma:

principles, protocols, and clinical applications. Emerg Radiol

23.

2006;13:7–18

8.

Newton PO, Hahn GW, Fricka KB, Wenger DR. Utility of three-

dimensional and multiplanar reformatted computed tomography

for evaluation of pediatric congenital spine abnormalities. Spine

24.

(Phila Pa 1976) 2002;27:844–850

9.

Mui LW, Engelsohn E, Umans H. Comparison of CT and MRI in pa-

tients with tibial plateau fracture: can CT findings predict ligament

25.

tear or meniscal injury? Skeletal Radiol 2007;36:145–151

10.

Lee E, Worsley DF. Role of radionuclide imaging in the orthopedic

patient. Orthop Clin North Am 2006;37:485–501

26.

11.

McCarthy EF, Frassica FJ. Diagnosing bone disease. In: McCarthy EF,

Frassica FJ, eds. Pathology of Bone and Joint Disorders: With Clinical

and Radiographic Correlation. Philadelphia: WB Saunders; 1998:1–24

12.

Abdel-Dayem HM. The role of nuclear medicine in primary bone and

27.

soft tissue tumors. Semin Nucl Med 1997;27:355–363

13.

Deutsch AL, Coel MN, Mink JH. Imaging of stress injuries to bone.

Radiography, scintigraphy, and MR imaging. Clin Sports Med

28.

1997;16:275–290

14.

Greenspan A, Stadalnik RC. A musculoskeletal radiologist’s view of

nuclear medicine. Semin Nucl Med 1997;27:372–385

15.

Alazraki NP. Radionuclide imaging in the evaluation of infections

29.

and inflammatory disease. Radiol Clin North Am 1993;31:783–794

16.

El-Maghraby TAF, Moustafa HM, Pauwels EKJ. Nuclear medicine

methods for evaluation of skeletal infection among other diagnostic

modalities. Q J Nucl Med Mol Imaging 2006;50:167–192

426

V Special Considerations

(e.g., iron, nickel, and martensitic stainless steel) concentrate

Implant Safety Profiles

and retain magnetism the most, resulting in severe distor-

The FDA requires testing of all implants to evaluate their

tion of the images. Paramagnetic or weakly ferromagnetic

safety profiles and classify them as MRI safe, condition-

materials (e.g., platinum) have a minimal e ect on mag-

ally safe, or unsafe. The list of these devices is extensive

netic field homogeneity and result in less image distortion.

and constantly changing, especially as more objects are

Diamagnetic materials (e.g., zinc, gold, and copper) do not

tested at 3 T and higher, precluding a complete review of

a ect or a ect only minimally the static or local magnetic

these devices in this chapter. A regularly updated list of re-

fields.

viewed implants and devices is available online at http://

Metallic Objects in Magnetic Fields

www.MRIsafety.com. It is important to be aware of devices

that absolutely contraindicate MRI scanning, including the

The clinical value of an MRI examination in a patient with

following:

metallic hardware depends on the proximity of the hard-

• Implantable cardiac defibrillators

ware to the site of interest. For example, one can anticipate a

• Cardiac pacemakers

limited evaluation of neural foramina adjacent to an anterior

• Implantable medication infusion pumps

cervical fusion or an inability to detect an epidural abscess

• Ferromagnetic aneurysm clips (e.g., stainless steel)

adjacent to pedicle screw instrumentation. Newer pulse se-

• Poppen-Blaylock carotid artery clamps

quences have been developed that allow for imaging in the

• Spinal/bone fusion stimulators

presence of metallic implants (see Chapter 16). Myelography

• Cochlear implants

remains a viable alternative for the postoperative spine. CT

• Tissue expanders

also is a valuable alternative in postoperative patients, par-

• Gastric electrical stimulation devices

ticularly in conjunction with myelography.

In addition to causing distortion of images, some metal-

Certain models of some devices (e.g., implantable cardiac

lic foreign bodies or surgical implants can move or gener-

defibrillators, cardiac pacemakers, spinal/bone fusion

ate heat in the presence of a magnetic field, possibly leading

stimulators, and cochlear implants) may be scanned under

to injury or death.9,10 For this reason, each patient must be

strict criteria. However, many MRI centers still consider as

screened for metallic objects within the body, usually with a

absolute contraindications the presence of such devices or

verbal interview and a written checklist.

of devices that do not meet the required technical condi-

Of particular concern are metallic foreign bodies within

tions (see below). Of note, the Starr-Edwards Model Pre-

the orbit that may dislodge and rupture the globe or dam-

6000 heart valve prosthesis (Baxter Healthcare, Santa Ana,

age the optic nerve. To our knowledge, there is only one re-

CA) is now designated as conditionally MRI safe, although

ported case of a patient who su ered a vitreous hemorrhage,

previously it was thought to be an absolute contraindication

caused by a dislodged metal fragment (2.0 × 3.5 mm), that

to an MRI examination.13 In recent years, multiple in vitro

led to blindness.11 Although it is standard for MRI facilities to

and in vivo controlled studies have shown increasing evi-

prescreen for metallic orbital foreign bodies, methods of ac-

dence that some patients with cardiac pacemakers can be

complishing this screening vary. Conventional radiographs

scanned safely under specific conditions, despite the poten-

of the orbits are said to detect metallic fragments as small as

tial for arrhythmia and death.14–18 However, in most situa-

0.1 × 0.1 × 0.1 mm. However, there is debate over which pa-

tions, a pacemaker remains an absolute contraindication for

tients should be referred for conventional radiographs. Many

MRI unless the procedure is an orchestrated e ort between

MRI centers obtain orbital radiographs of patients with an

cardiology and radiology, with informed consent of the

occupational history of welding, but some experts advocate

patient.19,20

obtaining films only if the patient is aware of a previous or-

Similar caution is warranted for patients with neurostim-

bital exposure to metal without removal of the fragment by

ulation systems for deep brain stimulation of the thalamus,

an ophthalmologist.12 At the authors’ institution, patients

globus pallidus, and subthalamic nucleus as a treatment for

with a history of working with metal undergo screening

movement disorders. Although many patients have been

orbital conventional radiographs. Alternatively, review of a

scanned successfully without incident, there are specific

previous CT scan, including the entirety of the orbits, is often

guidelines regarding the technique.21,22 Currently, the Pul-

considered su cient.

sar Cochlear Implant (MED-EL Corp., Durham, NC) can be

In addition to assessing for orbital foreign bodies, the cli-

scanned, but only under specific conditions on a 0.2-T ma-

nician should question the patient regarding any history of

chine. The Nucleus 24 Auditory Brainstem Implant System

metallic foreign bodies near other vital structures, such as

(Cochlear Corp., Englewood, CO) has a removable magnet

the lungs or spinal cord. For example, bullet fragments in the

and may be scanned up to 1.5 T, again under specific condi-

spinal canal contraindicate MRI because they may be ferro-

tions. It is suggested that the manufacturer of these cochlear

magnetic.

devices be contacted before imaging.23 In general, imaging of

deep-brain stimulators and this specific implant should be

Superficial Metal

performed only after discussion with a neurologist and radi-

There are safety concerns not only with internal metallic

ologist. There are six specific requirements that also must be

devices but also with skin surface metal, such as medicine

met to obtain an MRI study of a patient with a spinal/bone

patches containing a metal foil, surgical staples, tattoos,

fusion stimulator24,25:

• Cathodes of the implantable spinal fusion stimulator

or permanent cosmetics. It is standard practice to remove

transdermal medicine patches containing metallic foil at the

should be a minimum of 1 cm from nerve roots.

time of an MRI. Tope and Shellock31 reviewed the results of a

• Conventional radiographs should be obtained before

questionnaire given to 1032 patients with cosmetic tattoos.

MRI to verify that there are no broken leads for the im-

Only two patients experienced any sensory consequences

plantable spinal fusion stimulator.

(i.e., “slight tingling” or a “burning” sensation). These sen-

• The study should be obtained on an MRI system

sations are thought to be caused by heating from iron ox-

with static fields of 1.5 T or less, avoiding pulse se-

ide or other metal-based pigment. The FDA Center for Food

quences that expose patient to high levels of RF

Safety and Applied Nutrition, O ce of Cosmetics and Colors

energy.

fact sheet states, “The risks of avoiding an MRI when your

• The patient should be observed continuously.

doctor has recommended one are likely to be much greater

• To reduce artifact, the implantable spinal fusion stim-

than the risk of complications from the interaction between

ulator should be placed as far from the spinal canal and

the MRI and tattoo or permanent makeup.”32 Most prac-

bone graft as possible.

tices agree that an ice pack or cold compress can be applied

• Selected imaging techniques, such as the use of FSE

during scanning to the site of the tattoo, permanent cos-

pulse sequences, should be used to reduce artifact.

metics, or surgical staples to reduce the chance of thermal

In the past, residual pacing wires also were considered to be

injury.

a contraindication to MRI. However, the current consensus

is that such patients may undergo MRI if the wires are cut

External Metallic Objects

short (flush with skin) and there are no loops of wire outside

In addition to precautions about internal foreign bodies, MRI

the patient. Again, consultation with the patient’s cardiolo-

gist may be necessary.26

centers screen for external metallic devices that may become

Devices that are conditionally safe for MRI are implants

projectiles in the MRI suite. Injuries and death have occurred

that may be scanned if certain guidelines are satisfied.

when large metallic objects, such as a ferrous oxygen tank,

These devices include weakly magnetic intravascular fil-

have been brought into the MRI suite.33–35 Even small objects

ters, stents, and coils. MRI of patients with such devices

that may not seem dangerous to many patients, such as jew-

may require a waiting period of 6 to 8 weeks after implan-

elry or hairpins, can become projectiles and cause injury. It

tation to ensure that movement of the device caused by the

is standard procedure to ask patients to remove such objects

magnetic field does not disturb its implantation onto the

and to empty their pockets.

vessel wall.27,28 The evolving list of all such devices is be-

yond the scope of this chapter, but in general, one should

acquire additional information (e.g., brand name of the de-

■ Pregnancy

vice and date of implantation) for patients who have under-

gone recent placement of such devices. Many MRI centers

Although there are no known deleterious e ects of an MRI

require documentation of this information before scanning

examination during pregnancy, concerns about potential

is allowed.

side e ects remain. One such concern is that electromag-

Devices that are safe for MRI are those known to produce

netic fields could disrupt cell division. Because cell division

no clinically significant hazard in the MRI environment. In

is more rapid in the first trimester, it usually is acceptable to

general, these devices have no electronically or magnetically

delay MRI until after the first trimester.

activated component, are made from a nonferromagnetic

Because of such potential complications, MRI during

material (such as titanium or nitinol), and may undergo

pregnancy is obtained on a case-by-case basis, weighing

MRI scanning at ≤1.5 T immediately after implantation.29,30

the risk and benefit for each examination; this procedure

Many of these devices have been tested in the 3-T environ-

is the accepted standard of care advocated by the American

ment. It is important to obtain the brand name of the device

College of Radiology.36 Shellock and Kanal37 have suggested

from patients (who may have the package insert) or from

that “MR imaging may be used in pregnant women if other

their records. Safe devices also include orthopaedic implants

nonionizing forms of diagnostic imaging are inadequate or if

firmly placed within the bone because, although they may

the examination provides important information that would

be weakly magnetic, they do not dislodge or generate sub-

otherwise require exposure to ionizing radiation.” In almost

stantial heat.

all institutions, written, informed consent is obtained.

428

V Special Considerations

alysis within 2 days of gadolinium administration. The tim-

■ Contrast

ing of dialysis relative to gadolinium administration may be

MRI contrast agents are often used in the postoperative pa-

critical for the prevention of this disease, but thus far little

tient to evaluate for infection or scar tissue, in patients with

is known regarding the e ectiveness of dialysis in reducing

known or suspected musculoskeletal tumors, and for MR

the risk of nephrogenic systemic fibrosis.43 At the authors’

angiography of the carotid and peripheral arteries. The gad-

institution, a creatinine/estimated glomerular filtration rate

olinium ion contains seven unpaired electrons in the outer

measurement is currently obtained for patients at risk for

shell, providing a large magnetic moment. This paramag-

renal dysfunction, including those ≥65 years old or with a

netic property enhances the relaxation rates of nearby water

history of diabetes, those with renal disease or transplanta-

protons. Although gadolinium itself is toxic, chelation with

tion, and those with liver disease or hepatorenal syndrome.

other substances makes it nontoxic and usable as a contrast

In pregnant patients, contrast agents cross the placenta,

agent. Over time, within the body, the free gadolinium ion

enter the fetal collecting system, and then are excreted into

can dissociate from its chelate. Normally, the amount of free

the amniotic fluid. To the authors’ knowledge, no studies

ions is low because of rapid clearance through the kidney.

show the clearance rate of MRI contrast agents in the fetus,

In addition to screening for the specific populations listed

but it is possible that a chelated gadolinium agent could stay

within the amniotic fluid long enough to allow toxic free

ions to accumulate. Gadolinium-based intravenous MR con-

trast is labeled by the FDA as a category C medication; that

is, there is a lack of controlled studies with which to evaluate

the e ects. Contrast is generally not administered to preg-

nant patients unless the potential benefit outweighs its risks

and unless written, informed consent has been obtained.20,44

The theoretic risk of free ion accumulation is smaller if the

agent is administered toward the end of gestation in the

third trimester, leaving less time for dissociation and accu-

mulation of free ions before fetus delivery.

For patients with renal failure, there is concern that de-

When a breast-feeding mother receives contrast, it is

creased renal clearance may result in accumulating free ion

expected that most of the contrast will have cleared by 24

levels and toxicity. Clinicians usually recommend that a

hours, leaving minimal residual contrast (<0.04%) to be ex-

patient undergo dialysis within 24 hours after contrast ad-

creted into the breast milk.20,45 However, a breast-feeding

ministration. The FDA recently issued an alert for the use of

woman should be given the option to abstain from breast-

gadolinium intravenous contrast in patients with advanced

feeding for 24 hours and to pump and discard breast milk for

renal failure (i.e., those currently requiring dialysis or with an

this time period.

estimated glomerular filtration rate of <30 mL/min/1.73m2)

Other patient populations have a theoretic risk of toxic-

because of the risk of inducing nephrogenic systemic fibrosis/

ity from gadolinium, although no direct clinical evidence has

nephrogenic fibrosing dermopathy.39

been established. For example, patients with elevated levels

Nephrogenic systemic fibrosis/nephrogenic fibrosing der-

of copper (such as those with Wilson disease) or zinc may

mopathy is a progressive and sometimes fatal disease seen in

have increased free ion accumulation after contrast adminis-

patients with reduced renal function, and it causes fibrosis of

tration because these metals may compete with gadolinium

the skin and connective tissues throughout the body, includ-

for the chelate. In vivo studies suggest that gadolinium ad-

ing muscles of the extremities or abdomen, the diaphragm,

ministration can lead to vasoocclusive complications in pa-

and pulmonary vessels. Gadolinium has been detected in the

tients with sickle cell disease because deoxygenated sickle

soft tissues of several patients with nephrogenic systemic

erythrocytes align perpendicularly to a magnetic field.46,47

fibrosis who were exposed to it as a radiographic contrast

However, no clinical evidence suggests that these agents

agent, supporting its association with this disease.40 Deo et

precipitate a sickle cell crisis. Some facilities consider sickle

cell disease to be a contraindication to the administration of

for 18 months and found that each radiologic study that used

gadolinium.

a gadolinium-based contrast agent presented a 2.4% risk for

Physicians, both clinicians and radiologists, are often

nephrogenic systemic fibrosis. Broome et al42 reported an

faced with the decision to give gadolinium contrast to a pa-

odds ratio of 22.3 (95% confidence interval; range, 1.3 to

tient with a history of an allergy to ionic contrast agents,

378.9) for the development of nephrogenic systemic fibrosis

such as those used for CT. Studies have shown that patients

after gadolinium exposure in 168 dialysis patients. An impor-

with a history of an ionic contrast allergy are at a higher risk

tant observation in that study was that 10 of the 12 patients

for a reaction, as are those with asthma and multiple medi-

who developed nephrogenic systemic fibrosis underwent di-

cation allergies.38,48 Often, MRI centers will require consent